Effect of Heat Treatment of Wood Flour on the Water Absorption, Thickness Swelling and Impact Performance of LDPE/Red Balau Composites

Abstract

Red balau saw dust was heat-treated at 180°C and 200°C for one hour respectively, compounded with low density polyethylene (LDPE) at 20% and 37% by weight and molded in an injection molding machine. Samples were soaked in water for 147 days to test the water absorption and thickness swelling rates. The initial rate and the equilibrium water uptake values decreased with heat treatment. Furthermore, the thickness swelling of the composites were found to increase with time of immersion and wood content. A reduction in thickness swelling up to 18% and 31% was observed in composites made of wood flour heat treated at 180°C and 200°C respectively. Charpy impact tests revealed that composites made from heat treated wood flour have higher peak load (P) values when compared with the untreated samples. Similarly, the critical stress intensity factor or fracture toughness (Kc) of the composites increased in the wet samples relative to the dry-as-molded ones. This increment is proportional to the wood content, with composites loaded with 37 wt% wood flour heat treated at 180°C showing the highest value of 1.78 MPa.m0.5. Energy to failure (W) of the moisture saturated composites were generally lower than those of the dry-as-molded ones. Critical strain energy release rate or toughness (Gc) of the composites decreased generally with water absorption, with composites made from wood flour treated at 200°C exhibiting the lowest value. Therefore, utilizing heat treated wood flour in composites production can impart properties that is able to withstand moisture related applications.